In various types of controlled mechanisms, it is desirable to have an accurate reciprocating action provided for a power cylinder and/or piston rod device for moving a controlled article positively and rapidly through a predetermined distance. Furthermore, it is usually necessary to provide a substantially standard cylinder unit where the effective stroke of the control piston can be adjusted to meet various required operating conditions.
One prior art construction in U.S. Pat. No. 2,922,397 has an operating piston with an auxiliary movable piston head positioned on the piston rod for varying the piston stroke by variation in the operative effective length of the piston means in the unit.
The provision of pressurized liquids or fluids for use in cylinder systems from supply reservoirs is disclosed in U.S. Pat. No. 3,494,027 and U.S. Pat. No. 4,015,538; while the provision of a movable cylinder and a fixed piston rod communicating with a fluid source through a bore in the anchor means is shown in U.S. Pat. Nos. 3,568,559 and 3,577,831.
In constructions of the types provided heretofore, some appreciable leakage problems were involved inasmuch as two axially spaced pistons moved with the piston rod and both required sealing action in the cylinder, and also the cylinder required a barrel finish and the friction or break away force of these two piston devices was quite high.
There is a need in the art for a good piston and cylinder combination having an adjustable length stroke and wherein the apparatus is efficient to operate and relatively easy to maintain.